One of the techniques for achieving a higher degree of integration of a semiconductor device is to multilayer a wiring. When forming a multilayered wiring structure, an n-th wiring layer and an (n+1)-th wiring layer are connected to each other through a conductive layer, and films called “interlayer dielectric films” are deposited on an area other than the conductive layer. A representative interlayer dielectric film is an SiO2 film. With a view to realizing a higher speed of an operation of the device, a lower relative dielectric constant of the interlayer dielectric film has been recently demanded. In consideration of this demand, a fluorine-added carbon film (fluorocarbon film), which is a compound of carbon (C) and fluorine (F), has attracted attention. The fluorine-added carbon film can have a relative dielectric constant equal to or less than 2.5, for example, by selecting a material gas of a suitable kind. Thus, as compared with the SiO2 film of a relative dielectric constant around 4, the fluorine-added carbon film is considered to be a significantly efficient film as an interlayer dielectric film.
JP10-144667A describes an art for depositing a fluorine-added carbon film on a semiconductor wafer (hereinafter referred to as “wafer”), with the use of an electron cyclotron resonance (ECR) plasma-processing apparatus. Specifically, a gas for generating a plasma, such as Ar gas, is converted into a plasma by exciting ECR by an interaction of a microwave and a magnetic field. The plasma converts a material gas into a plasma, whereby a fluorine-added carbon film is deposited.
As described in JP10-144667A, since the fluorine-added carbon film is an organic film, a gas that etches the film also etches a resist film made of an organic material. Thus, when etching the fluorine-added carbon film on which the resist film is directly formed, a thickness of the resist film should be greater than that of the fluorine-added carbon film. Further, when the resist film is removed by ashing by means of an oxygen plasma, the fluorine-added carbon film is undesirably removed.
Thus, when the fluorine-added carbon film is etched, it is necessary to form a thin film serving as a hardmask on the fluorine-added carbon film. Silicon oxide and silicon nitride are known as a material for the film as a hardmask. However, use of these materials is disadvantageous in that a higher relative dielectric constant thereof increases a relative dielectric constant of the overall interlayer dielectric films.
The inventor has paid attention to, as a material for a hardmask, an oxygen-added silicon carbide (SiCO) film and a nitrogen-added silicon carbide (SiCN) film of a lower relative dielectric constant. The SiCO film is a silicon carbide film that contains about 20 atomic % of oxygen, and the SiCN film is a silicon carbide film that contains about 10 atomic % of nitrogen. In particular, the former SiCO film appears to be an effective film in view of the following advantages thereof. For example, the SiCO film is excellent in adhesion to a silicon nitride film and a silicone carbide film that function as a barrier layer for preventing diffusion of copper, when copper used as a wiring is embedded in the interlayer dielectric film. After the copper has been embedded, the interlayer dielectric film is subjected to a polishing process called CMP so as to remove the copper on the interlayer dielectric film. The SiCO film has a high resistance to the CMP.
However, there is a problem with the SiCO film. That is, when the SiCO film is deposited on the fluorine-added carbon film, a vapor (gas) of an organic compound, such as trimethyl silane, and oxygen gas are converted into a plasma. At this time, active species of oxygen react with the carbon contained in the fluorine-added carbon film to generate and release CO2. It is known that, when the fluorine-added carbon film is heated under an atmosphere where only a slight amount of oxygen such as 1 ppm exists, a degassing amount from the film is increased. Thus, denseness of a surface of the fluorine-added carbon film is decreased, which impairs an adhesion between the same and the SiCO film.
The SiCN film does not have a sufficient adhesion to the fluorine-added carbon film, although the SiCO film is worse, and thus there is concern that a yield is lowered. The reason therefor is supposed as follows: When the SiCN film is deposited, a vapor of an organic compound, such as trimethyl silane, and nitrogen gas are converted into a plasma. At this time, nitrogen in the plasma permeates the fluorine-added carbon film at an initial stage of the film deposition process. The nitrogen permeating the fluorine-added carbon film is released during the film deposition process, so that denseness of the fluorine-added carbon film is degraded. As a result, it is supposed that the adhesion between the SiCN film and the fluorine-added carbon film is deteriorated.